The present invention relates to a procedure for accelerating call setup in a wireless local loop.
In a wireless local loop (WLL, Wireless Local Loop or RLL, Radio in Local Loop), a terminal unit is connected via a wireless link to an access node (AN). The access node may consist of multiplexers, crossbar switches and various transmitting systems. The WLL system may be based, e.g., on technology used in mobile telephone systems, such as the GSM/DCS1800 technology (GSM, Global System for Mobile Communications; DCS, Digital Cellular System). GSM is a European digital mobile communication system standardised by ETSI. DCS-1800 is a mobile communication system standardised by ETSI, which is based on the GSM specification and aims at a more effective use of microcells and which works in the frequency range of 1800 MHz. Between the terminal unit and the access node there is a base transceiver station, through which call signals received from the terminal unit over a radio channel are transmitted via the access node to a public telephone network and vice versa. The access node can be connected to the telephone exchange using, e.g., a V5.2 protocol consistent with the ETS 300 347-1 standard or a V5.1 protocol consistent with the ETS 300 324-1 standard. The access node functions as a converter between GSM signalling and V5 signalling.
During call setup in a local loop, various checking functions related to network security management are carried out. The checking functions are designed to prevent illicit access to the network for users who have no right to use it, and to prevent the use of e.g. a mobile station reported stolen. The checking operations defined by the GSM specifications, carried out during call setup, retard the call setup process so that the V5 signalling time-outs are tripped and the call must be disconnected even though it is most likely to be successful. In a wireless local loop, fast setup of an outgoing call is particularly important.
An operation retarding call setup is, e.g., change of the subscriber identity code (TMSI reallocation), which means changing the temporary subscriber identity code assigned for the subscriber by the visitor location register and allowing confidential subscriber identification, e.g., during the call. Another check retarding call setup is the verification of the subscriber's access right, i.e., subscriber authentication, which means checking the subscriber data of a mobile station and preventing illicit access to the network. A third check retarding call setup is the verification of the subscriber's equipment identity code (IMEI check). To check the equipment identity code, it is compared with a register of equipment identity codes of mobile stations reported stolen and/or defective. IMEI is an international mobile station equipment identity code, by means of which a mobile station can be unambiguously identified.
Especially the time-outs in the PSTN protocol in the V5 interface (standard ETS 300 324-1 1 13) cause problems in call setup in a wireless local loop system. For instance, in the case of a terminating call, the time-out according to the V5 PSTN protocol between the start message and the acknowledgement message (the telephone rings) is max. 4 seconds (standard ETS 300 324-1 13.6).